An integrated circuit is typically manufactured by a process which utilizes planar technology. Generally, this process includes growing a layer of silicon dioxide on a silicon wafer. In addition, a photosensitive coating, or photoresist, is formed on the silicon dioxide layer. Ultraviolet light is then utilized to polymerize and harden predetermined areas of the photoresist. Areas of the photoresist not subjected to ultraviolet light are dissolved and removed, thus forming a photoresist mask on the silicon dioxide layer and leaving an exposed silicon dioxide surface in the shape of a desired circuit pattern. The exposed silicon dioxide layer surface is then subjected to hydrofluoric acid which removes the exposed silicon dioxide layer and exposes the underlying silicon wafer. Dopants are then diffused into the exposed silicon wafer which are ultimately used to form the desired circuit.
A photoresist coater apparatus is used to form the photoresist layer. Essentially, the photoresist coater is adapted to spin a silicon wafer inside of an associated cup element known as a "catch cup" while photoresist is applied to the silicon dioxide layer on the silicon wafer. Centrifugal force produced by spinning the silicon wafer spreads the photoresist and forms a relatively thin layer of photoresist on the silicon dioxide layer. Each catch cup serves to collect excess photoresist that is spun off of the silicon dioxide layer by the centrifugal force.
The performance of an IC or other similar electronic device is substantially degraded by particulate and other contamination. As such, many of the processes used for manufacturing an IC, such as coating the silicon dioxide layer with photoresist, are performed in a clean room having a filtration system. The filtration system serves to remove particles and other contamination from the cleanroom to provide a level of cleanliness suitable for manufacturing an IC. In addition, it is desirable that items used in the manufacture of ICs, such as catch cups, are also maintained at least at the same level of cleanliness as the device being manufactured in order that such items do not contaminate the device.
Typically, the catch cups are periodically removed from the photoresist coater in order to clean excess photoresist from the catch cups. In many manufacturing facilities, the catch cups are cleaned in a workroom which serves as a general purpose cleaning area where various other items in the facility are also cleaned. Consequently, substantial amounts of particulates and other contamination are generated in such workrooms. In addition, such workrooms typically do not include a filtration system or other similar equipment for removing such contamination.
An open cart is often used to transport the catch cups between the cleanroom and the workroom. Typically, the catch cups are placed on a shelf of the cart such that they are exposed to the surrounding environment. As such, the catch cups are subject to substantial amounts of contamination after they have been cleaned in the workroom. In addition, the catch cups are subject to further contamination by particles which have not been removed by the filtration system in the cleanroom. Still further contamination may result if a contaminated tool or other item is placed on the open cart near the catch cups. Consequently, the catch cups may be in a substantially contaminated condition before they are re-installed into the photoresist coater.
A substantial amount of turbulent air flow is generated by each silicon wafer as it spins within its associated catch cup during application of the photoresist layer. This air flow displaces particles and other contamination from its associated catch cup. Frequently, this contamination undesirably contaminates the photoresist, silicon wafer or both, ultimately resulting in an IC device having substantially degraded performance.
Furthermore, it is noted that photoresist emits odors which are offensive to many operators. As such, operators who transport catch cups contaminated with photoresist on the cart must frequently stop in order to seek relief from the odors, thus resulting in lost productivity. Consequently, there is a need in the art for a clean room cart which maintains the catch cups at a cleanliness level sufficient for IC manufacturing and which substantially reduces an operator's exposure to odors emitted by photoresist in the catch cups.